1. Field of the Invention
The present invention concerns a position sensor and, more specifically, it relates to a position sensor using a magnetic resistance element or magnetoresistive element.
2. Description of Related Art
A gear-access type rotary sensor utilizing a magnetic resistance element has been disclosed in Japanese Patent Application Laid-Open No. Hei 3-195970. In the sensor, as shown in FIG. 24, a magnetic resistance element 32 is vapor deposited on a substrate 31. The substrate 31 is attached vertically to a magnetized side 33a of a bias magnet 33. The substrate 31 (magnetic resistance element 32) is opposed to a gear 34 comprising a magnetic body, and a bias magnetic field is generated from the bias magnet 33 to the gear 34. Then, change of the bias magnetic field (change of the direction of a magnetic vector B) is detected as a change of resistance along with the rotation of the gear 34. That is, the direction of the magnetic vector B changes at every passage of a tooth 34a of the gear 34 in front of the substrate 31 (magnetic resistance element 32), and it is taken out as an electric signal (sinusoidal signal or rectangular signal).
The rotary sensor can not detect the rotational position during stopping of rotation. That is, although the sensor always detects the angle of rotation during rotation of the gear 34, it can not detect the rotational position (angle of rotation) during stopping of rotation.
As a result, if the rotary sensor is used as a cylinder discriminating sensor in an ignition timing control system for a multi-cylinder gasoline engine it brings about a disadvantage. That is, as shown in FIG. 25, a cylinder discriminating sensor is disposed near a crank shaft or a cam shaft, a gear having protrusions (teeth) is disposed at a predetermined angle to the shaft, and cylinder discrimination signals G1 and G2 are outputted at every predetermined angles (predetermined crank angles). However, the angle of rotation can not be recognized during stopping of the shaft and a cylinder can be determined only when the tooth of the gear passes after starting the rotation of the gear of the engine. Accordingly, ignition timing controlled by the discrimination of the cylinder is retarded, and ignition delay occurs in a first cylinder and a second cylinder in FIG. 25 to cause a problem that unburnt gasoline stagnated in the cylinders is discharged. In FIG. 25, the cylinder discriminating signal just after the start of the engine is canceled (masked) for preventing erroneous detection due to lowering of a battery voltage caused by driving of a starter motor.
As described above, since the conventional rotational angle sensor detects the change of direction of the magnetic vector along with the rotation of the gear, the rotational position in a stationary state can not be detected and ignition delay is caused upon starting or cranking the engine, for example, when it is used as a cylinder discriminating sensor in an ignition timing control system of the multi-cylinder gasoline engine. Thus, sensors capable of discriminating the cylinder even during stopping of the engine has been demanded.